Cholesterol in Animal Feed Formulation
Formulated Feed for Shrimp and Prawn Mass Culture and Feed Ingredients.
Formulated feed for shrimp and prawn mass culture is a very complex mixture of numerous ingredients from different sources specifically addressed to supply the nutrients and energy shrimp and prawn need for best growth. (FAO: www.fao.org/fishery). A complete feed is a formulated pellet that provides all required nutrients in the proper proportions necessary for rapid weight gain, high feed efficiency and necessary for shrimp and prawn health and quality.
Cholesterol, and the fatty acids eicosapentaenoic acid (EPA), docosahexaenoic acid (DHA), linoleic acid (LA), and alpha-linolenic acid (ALA) are among the several essential nutrients which cannot be synthesized by shrimp or prawn, so a dietary source is essential.
Typically, fish oils incorporated into the formulated pellet at 2 to 3 percent, provide the essential fatty acids EPA and DHA, meanwhile vegetable oils like soybean oil and linseed oil provide the essential fatty acids LA and ALA. Dietary requirements of EPA and DHA for shrimp and prawn range from 0.5 to 1.0 percent in the feed. The total lipid content of the formulated pellet should be in the range of 6 to 9%.
Fish oil also contains, on the average, about 1% of total (free and esterified) cholesterol but this does not suffice alone to satisfy the cholesterol requirements of shrimp or prawn, because fish oil which is included typically at 2 to 3% in the feed would contribute at most only 0.02-0.03% of cholesterol in the diet instead of 0.5 to 1.0%, which is the range of the dietary requirement of cholesterol for shrimp and prawn.
GB 489623 discloses a process for obtaining cholesterol from marine animal oils by subjecting the oil to fractionation through multiple sequential vacuum distillations at different temperature and pressure, wherein one or more of the distillate fractions comprise cholesterol, both free and esterified. Such fractions comprising cholesterol, if desired, may be further purified by methods such as saponification followed by extraction of non-saponifiable matter with a water immiscible solvent, concentration and crystallization.
An embodiment of the disclosed process is Example 1 of GB 489623, wherein clarified whale oil is subjected to molecular distillation at a temperature of 90° C.-220° C. and a pressure of about 0.001 to 0.003 mmHg. As the pressure is lowered and the temperature is raised, successive fractions amounting to 0.2 to 2% are withdrawn, such fractions comprising most of the free fatty acids, squalene and other volatiles. More fractions in proportions ranging from 0.5 to 10% are withdrawn between about 120° C. and 160° C., such fractions comprising free and esterified cholesterol. To a skilled person, it is evident that that no less than four consecutive distillations, each at some specific temperature and pressure, are required to arrive at a cholesterol rich fraction.
There are several disadvantages of the process disclosed by GB 489623. At present, fish oil is a valuable commodity due to its content of eicosapentaenoic (EPA) and docosahexaenoic (DHA) acid. Multiple distillations of fish oil increase the trans fatty acid content of the oil, and promote polymerization of unsaturated fatty acid, which in turn decreases the content of EPA and DHA. Multiple distillations also render the fish oil unsuitable for human or animal consumption.
On the other hand, present day fish oils contain a great variety of toxic and/or harmful anthropogenic contaminants like polychlorinated biphenyls (PCB), dichlorodiphenyltrichloroethane (DDT) and its metabolites, dibenzo-dioxins (PCDDs), and dibenzo-furans (PCDFs), poly-aromatic hydrocarbons (PAH), pesticides and their degradation products, also known as persistent organic pollutants or POP's, which are resistant to environmental degradation and thus bio-accumulate. Therefore, the distillate fractions comprising cholesterol will comprise as well one or more of such contaminants. The content of such contaminants in the distillate fractions will be even higher than in the fish oil. This fact, though evident, can be found in the prior art.
U.S. Pat. No. 7,678,930 discloses a process for obtaining a free cholesterol-reduced fish oil by vacuum stripping the oil. On the other hand, U.S. Pat. No. 7,718,698 discloses a process for decreasing the amount of environmental pollutants in fish oil, also by vacuum stripping the oil. These two patents have similar disclosures. Therefore, under conditions of vacuum distillation where environmental pollutants are removed, free cholesterol is removed as well and vice versa.
The distillate of the process of U.S. Pat. No. 7,678,930 has a level of toxic and/or harmful anthropogenic contaminants higher than the fish oil and its cholesterol content is no greater than 10%, therefore it is unsuitable as a source of cholesterol in formulated shrimp and prawn feed. The same can be said of the cholesterol concentrates obtained by the process disclosed in GB 489623, which is an additional disadvantage of such process.
U.S. Pat. No. 6,136,368 discloses the use of the residue or pitch in the distillation of crude fatty acids of animal origin obtained upon hydrolysis of fat of cattle, pigs, poultry, sheep or fish oil. The process would increase the cholesterol content up to 20 times the original cholesterol content. Although the process leads to a cholesterol containing ingredient less expensive than the high purity cholesterol currently utilized in the feed of farmed crustaceans, i.e. the 90% or more pure cholesterol produced from lanolin or sheep wool grease, it has several disadvantages. For example, in case fish oil was utilized, its hydrolysis leads to the splitting of the fish oil triglycerides, a valuable commodity by itself in the commercially less valuable free fatty acids and glycerol.
Concerning the pitch or residue of the distillation containing cholesterol, claimed in U.S. Pat. No. 6,136,368 as feed ingredient to feed crustaceans, it is questionable whether it could be useful for such purpose. In column 2, lines 60-65 of the patent it is said: “This residue 21 is called “pitch” and contains many sterols that have a higher boiling point than fatty acids and are part of the reason why the residue cannot be distilled. The pitch contains a number of substances that are not clearly defined, such as free fatty acids, polymerized fatty acids, sterols (vitamin E, cholesterol and other sterols), impurities, etc. The polymerized fatty acids and impurities give the pitch its typical black colour.”
A cholesterol containing ingredient, also containing polymerized fatty acids (presumably mostly polymerized polyunsaturated fatty acids) and a “number of substances that are not clearly defined” does not seem to be a good alternative to the cholesterol the shrimp and prawn farmers are currently using.
Currently the main commercial source of cholesterol used in the cultivation of crustaceans like shrimps and prawns is the non-saponifiable or alcoholic fraction of lanolin or wool wax comprising from about 25% to about 32% of cholesterol. However, such fraction cannot be utilized directly as feed ingredient in aquaculture because it contains a great variety of other sterols and uncommon fatty acids not found in marine or aquatic species, which constitute anti-nutritional factors (ANFs). In order to be utilized as feed additive, the cholesterol content of the alcoholic fraction of lanolin has to be increased to at least 90% in order to reduce or remove most such ANFs. The purification process of cholesterol from lanolin requires several process steps of high chemical demand (precipitation) and solvents (crystallization), yielding to high energy consumption for solvent recovery and environmental impact. This makes cholesterol the most expensive single ingredient for use in shrimp and prawn feeds. Its substitution by less expensive cholesterol like the cholesterol containing composition of the present invention would greatly contribute to the reduction of the feed cost which is currently about half of variable production costs in shrimp and prawn culture.
It is therefore an objective of the present invention to provide a process for obtaining from fish oil having a low free fatty acid content, a composition comprising at least 20% of cholesterol and the use of the composition in animal feed, especially in shrimp and prawn feed. The disclosed process thus produces a residual or processed fish oil of high-quality suitable for animal or human consumption or for the elaboration of EPA and DHA concentrates.